1. Field of the Invention
The present invention relates to a lead frame separating and conveying apparatus used for semiconductor devices.
2. Prior Art
There are two types of known systems for storing large numbers of plate-form workpieces such as lead frames, etc.
The first type is a horizontal positioning system (stacking system) in which a plurality of plate-form workpieces are stored one on the other with the workpieces being placed in a horizontal attitude or the flat surfaces being set in the horizontal direction. This system further includes two types: an uppermost-rank separating type, in which the plate-form workpieces are removed starting with the uppermost workpiece, and a lowermost-rank separating type, in which the plate-form workpieces are removed beginning with the lowermost workpiece.
An example of the uppermost-rank separating type is described in Japanese Utility Model Application Publication (Kokoku) No. 63-42529, and an example of the lowermost-rank separating type is described in Japanese Patent Application Publication (Kokoku) No. 6-76146.
In these types of plate-form workpiece storing systems, lead frames are placed one on the other so that their positions are shifted in the form of a staircase. Thus, the lead frames are prevented from sticking together and are separated reliably one lead frame at a time.
The second type of system is a vertical positioning system in which plate-form workpieces are lined up in the conveying direction with the width directions of the workpieces (or the surfaces of the workpieces) being oriented in a vertical direction.
Japanese Utility Model Application Laid-Open (Kokai) No. 58-20230 discloses an example of this system.
In this system, plate-form workpieces are lined up in the conveying direction and set on an inclined stand with the flat surfaces thereof oriented in a vertical direction, and the rear end of the line of plate-form workpieces is pushed by an inclined slider, so that the workpieces are dropped one at a time onto a belt conveyor.
In the case of the horizontal positioning system (stacking system), the overall weight of the stacked plate-form workpieces is concentrated in the lower portion of the stack; accordingly, parts having a sufficient strength must be used for supporting the workpieces, and as a result the cost of the apparatus tends to be high. Furthermore, especially in the lowermost-rank separating system, all of the plate-form workpieces must be removed at one time if there is a trouble with parts such as claws used for removing the workpiece, etc. or if plate-form workpieces with a defective shape are mixed with the non-defective workpieces.
In this regard, with the vertical positioning system, the removal of defective plate-form workpieces onto the belt conveyer is easier. However, since the plate-form workpieces are merely caused to slide over the inclined stand, plate-form workpieces that are stuck together are sometimes not separated. Furthermore, when the plate-form workpieces are pushed by the inclined slider, the bottom surfaces of the plate-form workpieces rub against the surface of the inclined stand so that frictional resistance is generated. As a result, a driving means that pushes the plate-form workpieces with a driving force which exceeds the combined force of this frictional resistance plus the weight of the plate-form workpieces due to the inclined stand is required. Thus, the cost of the apparatus increases for this reason as well.
Furthermore, when the plate-form work pieces on the inclined stand are dropped onto the belt conveyor so as to be conveyed by the belt conveyor, each plate-form workpiece is dropped onto the belt conveyor while the end portion of such plate-form workpiece is in contact with another plate-form workpiece on the inclined stand. As a result, the plate-form workpieces are scratched. Moreover, the plate-form workpieces on the inclined stand are pushed by the inclined slider and dropped naturally onto the belt conveyor by their own weights; accordingly, there is a danger that two or more plate-form workpieces are dropped continuously. Furthermore, since the plate-form workpieces are naturally dropped by the gravity, only the plate-form workpieces that are flat with no projections can be used in this vertical positioning system.